Methane-suppressing effect of myristic acid in sheep as affected by dietary calcium and forage proportion

Abstract

The efficiency of myristic acid (14:0) as a feed additive to suppress CH 4 emissions of ruminants was evaluated under different dietary conditions. Six sheep were subjected to a 6 × 6 Latin square arrangement. A supplement of non-esterified 14: 0 (50 g/kg DM) was added to two basal diets differing in their forage:concentrate values (1:1/5 and 1: 0/5), which were adjusted to dietary Ca contents of 4/2 and 9/0 g/ kg DM, respectively. Comparisons were made with the unsupplemented basal diets (4/2 g Ca/kg DM). The 14:0 supplementation decreased ( P < 0/001) total tract CH 4 release depending on basal diet type (interaction, P < 0/001) and dietary Ca level ( P < 0/05, post hoc test). In the concentrate-based diet, 14:0 suppressed CH 4 emission by 58 and 47% with 4/2 and 9/0 g Ca/kg DM, respectively. The 14:0 effect was lower (22%) in the forage-based diet and became insignificant with additional Ca. Myristic acid inhibited ( P < 0/05) rumen archaea without significantly altering proportions of individual methanogen orders. Ciliate protozoa concentration was decreased ( P < 0/05, post hoc test) by 14:0 only in combination with 9/0 g Ca/kg DM. Rumen fluid NH 3 concentration and acetate:pro-pionate were decreased ( P < 0/05) and water consumption was lower ( P < 0/01) with 14:0. The use of 14:0 had no clear effects on total tract organic matter and fibre digestion; this further illustrates that the suppressed methanogenesis resulted from direct effects against methanogens. The present study demonstrated that 14:0 is a potent CH 4 inhibitor but, to be effective in CH 4 mitigation feeding strategies, interactions with other diet ingredients have to be considered.